The invention relates to the field of geophysical survey, specifically to equipment deployed for marine geo-electrical survey, in particular, utilizing methods of induced polarization, magneto-telluric and/or seismic survey, and it is intended for prognosis of hydrocarbons deposits and deposits of other mineral products, as well as for exploration of the earth's crust structure.
Currently, bottom systems with different structures and designations are widely known and used for marine geophysical survey and researches. Particularly, there are bottom seismic systems (RU 24890); Deep-water bottom self-emerging seismic system ADC-8/Soloviev S. L., Kontar E. A., Dozorov T. A., Kovachev S. A.//Izvestiya of the Academy of Sciences of USSR, Earth Physics, 1988, No. 9, p. 459-460; Ocean Bottom Seismometer (OBS) Systems. Company Profile Project Companies Kieler Umwelt und Meerestechnik GmbH (K.U.M.), Signal-Elektronik und Nets Dienste GmbH (SEND), April 2002, 11 p.), on the base of an underwater module, that comprises a hermetic body, provided with a device for setting the module on the sea-bottom, inside this module an apparatus for registration of hydro-acoustic signals with corresponding filters, formers, transformers, information accumulators, synchronization circuit, power source, and a device for determination of orientation of the underwater module are provided.
The main disadvantage of such systems is impossibility of complete and adequate transmission of the changing ground parameters onto the signal measuring sensors, installed on the supporting tubular frame, equipped with metallic mechanisms for throwing away and pressing to the ground, that in combination with the presence of border ground-metal causes additional inaccuracies at the acoustic signals passage and finally results in insufficient accuracy of the survey. Moreover (besides that), the use of the mechanisms for throwing away and pressing to the ground is not sufficiently effective (enough) because of their complexity, absence of control on their installation, that results in the placement of measuring sensors block in loose ground of the sea-bottom, and consequently leads to a loss in the working capacity of those system.
There are known bottom seismic systems of Sevmorgeo State Company construction (publicity booklet of Sevmorgeo), of buoy-based and self-emerging type. The systems of both types have a three-component geophone in gimbals mount, and a hydrophone. The buoy-based systems have a good transmission coefficient in the geophones channels due to great mass of the body; however the systems of this type have limitations on the setting depth, high risk of loss of the system, and require a sufficiently complex descending and lifting technology. The self-emerging type system comprises a spherical hermetic body encapsulating geophones, a power source, a registering device, and an electronic block of an acoustic release system of an electrochemical type. The hermo-body provides a positive floating of the whole system. It is used for setting the system on the sea-bottom by fixing it with elastic (rubber) straps to a concrete load through the release system.
Such system structure ensures high technological effectiveness of the descending and lifting operations, while carrying out the work at depths up to 6000 meters. However, a high position of displacement sensors relatively to the sea-bottom and elastic fastening of the system to the load reduces sensitivity of the system to the displacement waves.
There is known a self-emerging electromagnetic system (described in U.S. Pat. No. 5,770,945), which has body that contains of two orthogonal inductive magnetic field sensors, and the system of measuring of horizontal components of the electric field comprising horizontal semi-rigid arms fastened to the body, each arm having length of five meters, with electrodes located at the end of the arm.
The disadvantage of such system is insufficient measuring accuracy, and a limited range of application. Besides that, the system structure requires a vacant place on the deck with the area no less than 100 sq. meters and special descending and lifting equipment.
Another disadvantage of all of the above mentioned bottom systems is that they allow measuring only a specific group of parameters, that is conditioned by differences in requirements for exploiting the bottom systems of different types. The reviewed science-technical literature did not mention systems that allowed taking the seismic parameters along with the electromagnetic and/or magnetic strata characteristics.
The most similar in its technical essence to the inventive solution claimed herein is a self-emerging system for electromagnetic measuring taught in U.S. Pat. No. 6,842,006. The system has a body, a floating block, information collecting system, a load, and a load release system. The bottom system comprises a system for measuring of the horizontal components of the electric field, and arms, being a part of the measuring system. The arms are five meters long and have a diameter about five centimeters with electrodes. They form two orthogonal dipoles capable of movement in the vertical direction, that simplifies carrying out the descending and lifting operations, since it doesn't require taking away the system from the vessel board at a distance exceeding the arms' length.
The system comprises inductive sensors (from one up to four) that are usually located closer to the end of arms, for reduction of influence of the system's magnetic masses onto the results of measuring the magnetic field.
The disadvantage of the system is that its deployment is limited to only measuring the magnetic field parameters. Moreover, taking away the system off the board with the arms, directed upright down, increases a probability of damaging the electrodes and inductive sensors in case when during operation the water flow does not have enough time to move the arms into the vertical position, or bends one or several arms under the load, in particular, during operation on shallow water.